File Storage, Calculated: Retention Periods, Binder Maths, Running Metres

Every office eventually asks the same question: how much shelf do the files actually need? The answer is more computable than most furniture questions, because three of its inputs are fixed by law and by DIN format. This article walks through the calculation, from retention periods to binder measurements to running metres, so the shelving decision becomes arithmetic instead of estimate. It describes the German rules; the logic transfers, the numbers may not.

What must be kept, and for how long

German commercial and tax law sorts business paper into three retention classes. Accounting records (invoices, bank statements, receipts) must be kept for eight years; this was shortened from ten by the Fourth Bureaucracy Relief Act and applies since 2025. Annual financial statements, opening balances and inventories stay at ten years. Commercial and business letters, sent and received, keep six years. In every case the clock starts at the end of the calendar year of the last entry, which is why archives thin out neatly by year-end: at the start of 2026, accounting records through 2017 can go.

Two practical notes belong beside the law. First, these are minimums, and documents relevant to open proceedings or audits keep beyond them. Second, the rules govern the documents, not the medium – digitised archives under proper procedures shrink the paper problem at its root. What follows applies to whatever paper remains, and in most offices that is still a wall's worth.

The binder arithmetic

The A4 lever-arch binder is a standardised object: about 32 cm tall, 28.5 cm deep, with spines of 80 or 50 millimetres. That yields the three numbers every shelf plan needs. Per running metre, about twelve wide binders stand comfortably with browsing slack. A full wide binder weighs around two to two and a half kilograms, so a metre of full binders comes to roughly 25 to 30 kilograms. And the shelf level itself needs about 35 cm of clear height and at least 29 cm of depth so binders stand fully supported without overhanging.

Now the volume estimate. Count the binders the business fills per year, a number most small offices know instinctively, and multiply by the retention years that apply to their contents. A practice filling twenty accounting binders a year, kept eight years, carries 160 binders at steady state: a touch over thirteen running metres, before adding the ten-year and six-year classes and the working files that never leave the desk's reach. Steady state is the useful concept here: after the first full cycle, one year's worth enters and one leaves, and the archive stops growing.

From running metres to a wall

Translating metres into furniture is where the earlier shelf-zone logic returns. On a 75 cm section, one level holds about nine wide binders, which at full weight sits neatly at the 20 kg a KUUDU board carries; the format and the load limit happen to agree. The archive years belong on the lower levels: heavy, rarely touched, and in the stooping zone where closed boxes keep the room calm. The current year lives between 80 and 170 cm, in grasp and sight range. The top levels take the light classes – correspondence, documentation, the six-year letters.

A worked example: 160 archive binders need eighteen levels of nine, which three 75 cm sections of six binder-levels provide at about 215 cm height. That is one wall segment, not a storage room – the calculation usually surprises in the friendly direction. The law-office page and the office shelving page both start from configurations built on this arithmetic, with full-depth binder rows below and half-depth reference above.

Weight deserves a paragraph of its own. Thirteen running metres of full binders is the better part of 350 kilograms, standing in one room, often along one wall. Any decent shelving carries it level by level, but floors and fixings feel totals: spread archive walls across sections rather than stacking one tower to the ceiling, keep the heaviest years lowest, and if an archive wall stands on a wooden beam ceiling in an old building, that total is a question for a structural engineer rather than a furniture page.

One closing habit from records management: label the retention end year on the spine, not the start year. A binder that says 2033 answers its own question every time someone weeds the archive, and the annual clear-out becomes reading instead of arithmetic.